Secondary metabolites (SMs) play a crucial role in plant defense mechanisms against both abiotic and biotic stresses. These metabolites are synthesized in response to stress signals, which regulate the expression of genes involved in their production. The type and amount of SMs produced depend on the plant's genetic makeup, making them either resistant or susceptible to stress. SMs serve various functions, including acting as deterrents, allelochemicals, toxins, or precursors of other metabolites that protect plants from stress. Some pathogens may use SMs as signals for host recognition or nutrition rather than as toxins. Different SMs activate specific signaling pathways, such as terpenoids modulating the calcineurin pathway, sesquiterpenoids modulating the jasmonic acid and salicylic acid pathway, polyphenols activating the jasmonic acid and phenylpropanoid pathway, and alkaloids activating the salicylic acid pathway. These pathways help protect plants against pathogens and herbivores. Polyphenolic compounds provide resistance to various microbes by altering membrane permeability, cell wall integrity, and enzyme activity. Flavonoids help plants sustain pathogen stress by changing auxin transport. Pathogen exposure upregulates genes involved in alkaloid synthesis, leading to increased alkaloid accumulation. Plant exposure to pathogens triggers hypersensitivity reactions and phytoalexin accumulation. Salicylic acid and jasmonic acid treatments upregulate downstream transcription factors, increasing defense protein expression and SM synthesis, providing resistance against multiple pathogens. Pathogens and herbivores have coevolved to detoxify SMs, converting toxins into useful products, and adapting to SMs. This review provides molecular insights into the genes and regulatory proteins controlling SM synthesis, which may help understand the role of biosynthetic pathway intermediates and resistance genes. The article describes the roles of different SMs in plant defense and their molecular mechanisms. SMs have a significant role in plant evolution and contribute to allelopathy, influencing the growth and development of organisms. The review also discusses the molecular mechanisms of action of SMs and biotechnological interventions for plant defense. The article provides a comprehensive description of the role of SMs against both biotic and abiotic stresses, including their genetic regulation and enzymatic pathways.Secondary metabolites (SMs) play a crucial role in plant defense mechanisms against both abiotic and biotic stresses. These metabolites are synthesized in response to stress signals, which regulate the expression of genes involved in their production. The type and amount of SMs produced depend on the plant's genetic makeup, making them either resistant or susceptible to stress. SMs serve various functions, including acting as deterrents, allelochemicals, toxins, or precursors of other metabolites that protect plants from stress. Some pathogens may use SMs as signals for host recognition or nutrition rather than as toxins. Different SMs activate specific signaling pathways, such as terpenoids modulating the calcineurin pathway, sesquiterpenoids modulating the jasmonic acid and salicylic acid pathway, polyphenols activating the jasmonic acid and phenylpropanoid pathway, and alkaloids activating the salicylic acid pathway. These pathways help protect plants against pathogens and herbivores. Polyphenolic compounds provide resistance to various microbes by altering membrane permeability, cell wall integrity, and enzyme activity. Flavonoids help plants sustain pathogen stress by changing auxin transport. Pathogen exposure upregulates genes involved in alkaloid synthesis, leading to increased alkaloid accumulation. Plant exposure to pathogens triggers hypersensitivity reactions and phytoalexin accumulation. Salicylic acid and jasmonic acid treatments upregulate downstream transcription factors, increasing defense protein expression and SM synthesis, providing resistance against multiple pathogens. Pathogens and herbivores have coevolved to detoxify SMs, converting toxins into useful products, and adapting to SMs. This review provides molecular insights into the genes and regulatory proteins controlling SM synthesis, which may help understand the role of biosynthetic pathway intermediates and resistance genes. The article describes the roles of different SMs in plant defense and their molecular mechanisms. SMs have a significant role in plant evolution and contribute to allelopathy, influencing the growth and development of organisms. The review also discusses the molecular mechanisms of action of SMs and biotechnological interventions for plant defense. The article provides a comprehensive description of the role of SMs against both biotic and abiotic stresses, including their genetic regulation and enzymatic pathways.